Sawtooth wave generator



Feb. 15, 1949.

1.. L. JOHNSON 2,462,024

SAWTOOTH WAVE GENERATOR Filed Aug. 16, 1947' m I-i- N :J

K r I -*{:|||+|II I INVENTOR.

LAMBERT L. JOHNSON By %%%M ATTORNEY Patented Feb. 15, 1949 tJNE'l'ED SAWTOOTH WAVE'GENERATOR Lambert L. Johnson, Fort Wayne, Ind, assignojr, by mesne assignments, toFarnsworth-Research Corporation, a corporationof Indiana Application Aug'ustlG, 194.7, Sc1'ial No. 7 695037 This invention relates to saw-tooth wave generators, and particularly to generators of this character capable of producing substantially linear saw-tooth waves.

In the operation of many devices such as cathode ray tubes, it is necessary to generate sweep voltages which vary in amplitude substantially in a saw-tooth manner. It is generally desirable that the saw-tooth wave shape be substantially linear throughout the entire cycle. Many saw-tooth generators of the prior art have been capable of producing saw-tooth waves which are linear throughout only a portion of the signal. Consequently, it has been necessary to design the appartus in such a manner that only the substantially linear portion of the sawtooth Wave is used. Such apparatus is not capable of operating at maximum eificiency and'furthermore, it is not possible to derive a saw-tooth wave which has sufiicient amplitude to operate satisfactorily in many circuits.

However, there has been devised a saw-tooth wave generator which is capable of developing a saw-tooth wave of considerable amplitude and of substantial linearity throughout the entire cycle. As in many relaxation oscillators for developing saw-tooth waves, this device operates by alternately charging a condenser at -a relatively slow rate and discharging-it at a relatively rapid rate. The condenser voltage is employed to excite the grid of a vacuum tube arranged' as a cathode follower. The cathode voltage is impressed upon the condenser charging circuit in a manner to maintain the charging current substantially constant and. thereby linearize the output voltage.

The cathode follower voltage is impressedupon the condenser charging circuit by 'means of a back coupling condenser. In'order for the device to operate successfully, the impedance of the cathode follower circuit must be relatively high. During retrace periods of the saw-tooth wave, the coupling condenser must be discharged through the relatively high impedance of the cathode follower circuit. Such an arrangement results in a relatively slow discharge rate of the coupling condenser because of the relatively long time constant of'the condenser discharging circuit. Consequently, it has not been possible to successfully employ a saw-tooth wave generator of this character where relatively short retrace periods of the saw-tooth wave are necessary.

It is an object of the present invention therefore, to provide a substantially linear saw-tooth Wave generator of the character described in 7 Claims. (Cl. 250-36) 2 which the retracexperiods of the saw-tooth wave are materially shortened.

Another object of the: present invention is to provide, in :a saw tooth wave generator of the character describeda relatively low impedance discharge circuit'f'or the back-couplingcondenser whereby to shorten the retrace periods of the saw-tooth wave.

In accordance with the instant invention, there is provided a saw-tooth wave-generator having an energy storage condenser coupled-to a charging circuit including an' impedan'ce device. The terminals of the impedance device are coupled to the input circuit of a cathode follower tube.

Thecathode followertube'is arranged tohave a gain of approximate unity :whereby asubstantially constant voltage difier'ence i-s maintained across the chargin impedance device. The coupling circuit between the impedance device and the cathode follower tube includes a condenser associatedwith the cathode follower circuit. The apparatus also includes a discharge circuit of :relatively low impedance during 1 retrace =periods butwhich normally during trace periods has a--relatively=highimpedance. One means of providing such a circuit is by including a vacuum tube forthe storage-condenser which is periodically rendered conducting to discharge the storage condenser. in -accordance withan important feature ofthe presentinvention, there is provided "a similar discharge circuit which may include another vacuum tube-connected to the cathode follower circuit in such a manner I asto provide a relatively low-impedance discharge path for -the' coupling condenser. This vacuum tube also is rendered conducting concurrently with the discharge tubefor-the storagecondenser.

For -a better-understanding of the invention, together with other and further objects thereof, reference is had-to the f allowing-- description taken in connection with the accompanying drawing, and its scope will be pointed out inappended claims.

In the'accompanying drawingthe 'singlefigure is a schematiccircuit diagram of asaw-tooth wave generator embodying the:present invention.

Having reference now to'the drawing, there-is provided a charge storage condenser 1 connected into a charging circuit which-includes a diode-=2, a fixed resistor 3, :and a 'variable resistor 4. Charging current for the-condenser his: provided by a source of unidirectional current sucha-s -a battery '5, the negative terminal of :which is grounded and the positive terminal'of which-"is connected to the anodeofthediode-Z.

the battery 5. The screen grid is bypassed to the cathode by means of a condenser 9. The suppressor grid of this tube is connected to the cathode. The control grid of the tube 6 is coupled to the lower terminal of the charging resistor 3. The cathode of the tube 6 is coupled by a condenser II to the upper terminal of the resistor 3.

The storage condenser I is provided with a discharge circuit which includes a vacuum tube I2.

The discharging tube I2 is controlled by means of impulses derived from a source such as the synchronizing signal source I3. The synchronizing signal implses are impressed in negative polarity upon the control grid of an amplifier tube I4 by means of a coupling condenser I5 which is provided with a leak resistor I6. The screen grid of the amplifier tube is provided with a positive potential by means of a connection which includes a resistor I! to the positive terminal of the battery 5. The screen grid is bypassed to the grounded cathode of the tube by a condenser I8. The suppressor grid of the amplifier tube is directly connected to the cathode. Space current for the tube I4 is supplied from the battery 5 by means of a circuit which includes a load resistor I9. The output circuit of the amplifier tube I4 is coupled by means of a condenser 29 to the control grid of the discharge tube I2. The coupling condenser is provided by a leak resistor 2I.

There is also provided, in accordance with this invention, another vacuum tube 22, the anodeto-cathode circuit of which is connected in parallel with the cathode follower resistor I. This vacuum tube serves to discharge the coupling condenser II and for this purpose is rendered conducting concurrently with the discharge tube I2 by means of a coupling including the condenser I9 from the output circuit of the amplifier tube I l to the control grid of the tube 22.

An output circuit 23, is connected to the terminals of the cathode follower resistor I.

Having reference now to the operation of the improved saw-tooth wave generator, it will be assumed that a cycle of operation begins at the initiation of a trace period of the saw-tooth wave. At this time, the amplifier vacuum tube I4 is-in condition to conduct space current through the load resistor I9, whereby to depress the voltage of the anode with respect to ground sufiiciently to bias the discharge tubes I 2 and 22 sufliciently beyond the point of space current cut-oil to render these tubes nonconducting. Also, it is assumed that condensers I and II are completely discharged. The conden er I begins to charge at a relatively slow rate which is determined by the time constant of the circuit including the diode 2 and the charging resistors 3 and 4. The rate of charging may be adjusted by a variation of the resistor 4. As the condenser I accumulates a charge, the terminal thereof which is connected to the lower terminal of the resistor 3, increases in positive polarity relative to ground.

The increadng positive potential is impressed upon the control grid of the cathode follower tube 6, thereby correspondingly increasing the flow of space current in this tube. As the space current in the tube 6 increases in amplitude, the traversal of the cathode follower resistor 1 increases the potential of the cathode positively relative to ground. By employing as the resistor I one of the suificiently high impedances, the gain of the tube ii may be made substantially unity. Consequently, the control grid and cathode of the tube 6 increase in positive potential at approximately the same rate. The increasing positive potential of the cathode is impressed, by means of the coupling condenser II, upon the upper terminal of the charging resistor 3. By this means the voltage across this resistor is maintained substantially constant. As a consequence, the charging current forthe condenser is also maintained substantially constant. Such an arrangement insures that the rate of current increase through the cathode follower tube 6 is substantially constant. Therefore, the traversal of the resistor l by this current results in the development of a voltage across this resistor which is substantially linear.

At the end of the trace period produced by the operation of the apparatus described up to this point, a negative impulse derived from the source I3, is impressed upon the control grid of the amplifier tube I4 whereby to reduce the amplitude of the space current flowing in this tube. As a consequence, a positive impulse is developed at the anode of the tube I4 for impression upon the control grids of the discharge tubes I2 and 22. This impulse is of suflicient amplitude to reduce the impedance of these tubes substantially to minimum values. The charge storage condenser I,

5' therefore, is quickly discharged through the tube I 2. At the same time, the charge which has been acquired by the coupling condenser II is quickly dissipated through the tube 22.

Thus, the apparatus is restored to its originally assumed condition. Both the condensers I and II are discharged in a relatively short period of time. Consequently, as soon as these condensers are discharged, the following trace period of the saw-tooth wave may be started. In apparatus of this general character used heretofore the storage condenser I has been capable of being discharged rapidly so that, as far as this condenser was concerned, the following trace period of thesaw-tooth wave could be initiated. However, since the coupling condenser II had to be discharged through the relatively high impedance path including the cathode follower resistor l, a longer time was required to completely discharge the coupling condenser. Consequently, it was not possible to initiate the succeeding trace period of the saw-tooth wave as soon as the storage condenser I was completely discharged. By means of the present invention, however, the tube 22 provides a relatively low impedance discharge path for the coupling condenser II enabling the discharge of this condenser approximately as quickly as'the storage condenser I can be discharged. Therefore, it is seen that the present invention provides a means for considerably reducing the proportion of the saw-tooth wave cycle required for the retrace. Apparatus embodying the present invention accordingly is able to operate at a considerably greater efficiency than prior art apparatus.

While there has been described what is, at present, considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and, it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A saw-tooth wave generator comprising, a storage condenser, a charging circuit for said storage condenser including an impedance device, a vacuum tube having an input circuit including a control grid electrode and a cathode electrode, an impedance device connected in circuitwith said cathode electrode, means including a condenser for coupling the terminals of said charging circuit impedance device respectively to said input circuit electrodes, whereby to maintain a relatively constant voltage across said charging circuit impedance device, a discharge circuit for said storage condenser including means normally having a relatively high impedance, a discharge circuit for said coupling condenser including means normally having a relatively high impedance, and means for periodically reducing the impedance of said discharge circuits, means whereby to discharge said condensers associated respectively therewith.

2. A saw-tooth wave generator comprising, a storage condenser, a charging circuit for said storage condenser including an impedance device, a first vacuum tube having an input circuit including a control grid electrode and a cathode electrode, an impedance device connected in circuit with said cathode electrode, means including a condenser for coupling the terminals of said charging impedance device respectively to said input circuit electrodes, whereby to maintain a relatively constant voltage across said charging circuit impedance device, a discharge circuit for said storage condenser including a second vacuum tube, a discharge circuit for said coupling condenser including a third vacuum tube, and means for periodically rendering said second and third vacuum tubes conductive, whereby to discharge said condensers associated respectively therewith.

3. A saw-tooth wave generator comprising, a storage condenser, a charging circuit including an impedance device connected to said storage condenser, a cathode follower vacuum tube having a control grid and a cathode, an impedance de- Vice connected in circuit with said cathode, means for coupling one terminal of said charging impedance device to the control grid of said cathode follower vacuum tube, means including a condenser for coupling the other terminal of said charging circuit impedance device to the cathode of said cathode follower vacuum tube, a discharge circuit for said storage condenser including a second vacuum tube, a discharge circuit for said coupling condenser including a third vacuum tube, and means including a source of impulses coupled to said second and third vacuum tubes for periodically rendering said second and third vacuum tubes conductive, whereby to discharge said condensers associated respectively therewith.

4. A saw-tooth wave generator comprising, a storage condenser, a charging circuit for said storage condenser, a cathode follower vacuum tube having an input circuit including a control grid electrode and a cathode electrode, an impedance device connected in circuit with said cathode electrode,- means for coupling one terminal of said charging circuit impedance device to one of said input circuit electrodes, means including a condenser for coupling the other terminal of said charging circuit impedance device to the other of said input circuit electrodes, a discharge circuit for said storage condenser including a second vacuum tube, a discharge circuit for said coupling condenser including a third vacuum tube, and means coupled to said second and third vacuum tubes for periodically rendering said second and third vacuum tubes conductive, whereby to discharge said condensers associated respectively therewith.

5. A saw-tooth wave generator comprising, a storage condenser, a charging circuit including an impedance device connected in series with said storage condenser, a cathode follower vacuum tube having a control grid and a cathode, an impedance device connected in circuit with said cathode and being of sufficient magnitude to produce an amplification factor of said cathode follower tube equal substantially to unity, means for coupling one terminal of said charging circuit impedance device to the control grid of said Cathode follower vacuum tube, means including a condenser for coupling the other terminal of said charging circuit impedance device to the cathode of said cathode follower vacuum tube, a discharge circuit for said storage condenser including a second vacuum tube having a control grid, a discharge circuit for said coupling condenser including the space discharge path of a third vacuum tube having a control grid, and means coupled to the control grids of said second and third vacuum tubes for periodically rendering said second and third vacuum tubes conductive, whereby to discharge said condensers associated respectively therewith.

6. A saw-tooth wave generator comprising, a storage condenser, a charging circuit including a resistor connected in series with said storage condenser, a first vacuum tube having a control grid and a cathode, a resistor connected in circuit with said cathode and having a sufficiently high impedance to produce an amplification factor of said tube equal substantially to unity, means for coupling one terminal of said charging circuit resistor to the control grid of said first vacuum tube, means including a condenser for coupling the other terminal of said charging circuit resistor to the cathode of said first vacuum tube, a discharge circuit for said storage condenser including a second vacuum tube having a control grid, a discharge circuit for said coupling condenser includin a third vacuum tube having a control grid and being connected in parallel with said cathode resistor, and means including a source of impulses coupled to the control grids of said second and third vacuum tubes for periodically rendering said second and third vacuum tubes conductive, whereby to discharge 'said condensers associated respectively therewith.

'7. A saw-tooth wave generator comprising, a storage condenser, a charging circuit including a resistor connected in series with said storage condenser, a first vacuum tube having acontrol grid and a cathode, a resistor connected in circuit with said cathode and having a sufiiciently high impedance to produce an amplification factor of said tube equal substantially to unity, means for ammonicircuit" for said coupllng condenser 'i pcluding a" REFERENCESecflEfim thudwauumtube havmg a control grld ancl alsohaving t space-djscharge path connected n The followmg reference larenof-recorddxvthe; parallel with said cathode resistor, and. means file of thls patent: including 2. source of impulses coupled to the UNITED STATES control gnds of sald second and'third vacuum 2 2 tubes for periodically rendering said second and Numb Name 1 e l thirdva'cuum tubes simultaneously conductive, 2333376 m" whereby .to discharge szliclcondensers associated 1 respectively therewith; 10 2,412,064 MOB m.- D60. 3,;194 6 2,426,256 Zenor 1.2 Aug. 26,; 1941 LAMBERT L JOHNSON 2,431,766 Miller et all; D80. "2, 1947 a 

